Separating membrane with improved adhesion and process for obtaining it

ABSTRACT

Separating membrane of plastic material, made up of a bossed and waterproof sheet which is coupled with a permeable base layer. The bosses are of the cylindrical type with a double diameter and have such a shape and arrangement as to feature improved adhesion on both faces. The gripping of the adhesive is increased in order to obtain greater tear strength, on the upper face, and at the same time increases the area of contact with the base layer for a greater resistance to delamination on the lower face. In particular, inside each chamber there is an internal crown, which divides it like a necking into two superimposed compartments having the same diameter, wherein the first compartment has a depth amounting to at least ⅓ of the total. A production process for obtaining the membrane is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a division of U.S. patent application Ser.No. 15/528,676, filed on May 22, 2017, presently pending.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIALS SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a separating membrane, of plasticmaterial, of the type with bosses with improved adhesion both on theupper face, towards the cement adhesive, and on the lower face, towardsthe base layer; the present invention also relates to the productionprocess for obtaining said membrane.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 37 CFR 1.98

The present invention finds particular application in the buildingindustry and in particular in the sector of semi-finished components forbuilding such as, as a non-exhaustive example, the thin membranes whichare intended to separate the screed from the flooring; the membraneaccording to the invention, more generally speaking, is suitable for theworks of civil or environmental engineering, also in combination withother materials.

Nowadays, in the building sector various types of membranes are known,which have various purposes: for example, one should remember the vapourmembranes, the bituminous waterproofing membranes, the drainagemembranes, the geomembranes or even the separating sheets of nonwovenfabric. In particular, in modern building the waterproofing membranesare widely known, which are commonly applied by the layers of ceramiccoatings, of marble slabs or anyway of coatings of the fragile type, inorder to prevent cracks and detachments; such problems, in fact,sometimes occur in case of differentiated thermal expansions of thelayers, or due to the movements of the floor, due to foundationmicrosubsidences or for any deformation of the supporting plane which isnot correctly followed by the coating layer. A membrane, which isintended to prevent such problems, is conventionally called a separatingmembrane, or uncoupling membrane or even separating plate, beinginterposed like a diaphragm between the load-bearing structure and saidcoating in order to prevent its direct adhesion, to disperse stressesand to absorb deformations; to this purpose, particularly effective arethe waterproof membranes of the bossed type which separate more thelayers, distribute the point loads in a uniform way and also compensatefor the vapour stresses of the subfloor.

Therefore, in professional practice it has been observed that today themost used solutions provide waterproof membranes of the bossed type,used on their own or coupled with a permeable fabric layer. In moredetail, widespread are the sheets with small-sized bosses obtained onthe surface in a continuous way, like cylindrical protrusions, orprotrusions shaped as a truncated cone or a truncated pyramid arrangedin a regular matrix, which, being intended to increase the distancebetween the layers, and also being intended to improve stability andadhesion, allow the cement adhesive, which is in contact with saidsheet, to penetrate the interstices between the bosses or the cavitiesinternal to the protrusions themselves, according to the positioningdirection.

By way of example, the single-layer bossed sheets are widely used inunderground constructions, as an element of external protection andwaterproofing from the ground, and also in said cases of ceramic pavingon floors of reinforced-concrete, of wood or in the screeds on theground floor. However, for some applications, for example for a moreeffective drainage or to increase said separating function, the bossedsheet is also coupled with a base layer of permeable fabric, such as anonwoven fabric of polypropylene of the type called spunbonded orspunlace; in particular, in the separating use on a reinforced-concretescreed, it is well known that such a base layer adheres well to theunderlying adhesive interpenetrating it and also helps to compensate forthe differentiated movements between said screed and the flooring abovethe bossed sheet. For example, see the drawings of the known prior art(FIGS. 1 a-c ) which represent a conventional separating membrane madeup of a waterproof sheet provided with hollow bosses, of a cylindricalshape and arranged in a regular pitch matrix, which is also coupled onthe lower side with a base layer of the permeable type of nonwovenfabric.

From the production point of view, a membrane of the bossed type isindustrially obtained by extruding a sheet of plastic material which isthen formed on a roller whose surface is provided with protrudingbosses, which is also called bossed forming roller. In more detail as tosaid extrusion, there is a gravimetric feeding system which, in anautomatic way, doses the raw materials directly on the hopper throughwhich they enter the extruder; it, generally, is a heated cylinderinside which there is a worm screw that transports the melted materialto the head section. Therefore, the melting of the plastic materialoccurs inside said extruder, where the temperature is not uniform, itbeing generally between 185° C. and 290° C. according to the passagezone of the melted material; the flow of said melted material is thendistributed over the entire width of said head, and with the desiredweight, by means of particular deviation lips which are spaced apart inan adjustable way according to the desired product. Along the screw agrowing pressure is generated, from the hopper to the head, excluding adepression zone induced by a different section of said screw whichallows to extract any possible volatile substances; moreover, beforebeing cast around the forming roller, said melted material meets somefiltering stations intended to block any possible impurities.

The so melted plastic material by means of a depression is cast andadheres temporarily to the bossed surface of the roller in such a way asto assume the same bossed shape and also to replicate the same smoothsurface in the zones included between one boss and another boss. Theshape, the height and the pitch of the bosses which characterize thefinished product can be easily varied, by replacing from time to timesaid bossed forming roller with a specific roller structured in thedesired way. Then the so formed membrane passes through some thermalconditioning cylinders, towards an accumulator mount, to be finallyconveyed to the cutting, rolling and packaging zone. If a base layer isalso provided, said nonwoven fabric can be advantageously coupled duringthe manufacturing process of the sheet, for example by conveying italready stretched on the just made product in such a way as to exploitthe residual heat of the sheet and realize several heat melting points,that is to say, in correspondence of the head of the bosses; as analternative, it is possible to cold glue the fabric by means ofadhesives laid in strips or dots.

The most suitable raw materials for this type of working are the resinsof the type called olefins, and in particular polyethylene, which can below-density, medium-density or even high-density, being called by theLDPE, MDPE and HDPE acronyms, respectively; as an alternative,polypropylene, known by the PP acronym, or thermoplastic polyolefins,known by the TPO acronym, are suitable as well. In some casespolystyrene, known by the PS acronym, is also used. Such raw materialscan be either virgin or regenerated, the latter being derived from therecovery of products in the post-production or post-consumption phase.

In general, those skilled in the art know that a membrane with anuncoupling function, particularly of the type with a bossed sheet joinedon the lower side to said base layer, generates the above-describedadvantages but also produces a considerable decrease in the values ofadhesion between the flooring and the screed. In particular, both theadhesion between the bossed sheet and the overlying cement adhesive, andthe adhesion between said bossed sheet and the base layer of nonwovenfabric are weak; on the other hand, the adhesion of said base layer tothe underlying cement adhesive is solid and effective.

In more detail, as to the adhesion of the adhesive mortar to said sheet,it has been observed that the known and conventional solutions availableon the market do not allow for a suitable adhesion to the bossed sheetof the bedding layer of the flooring and particularly in the light ofthe new building regulations, such as the UNI EN 1348 European standardof 2000, which specifically requires each cement adhesive on ceramictiles to resist at least at 0.5 N/mm² following the test at 28 days,also called initial adhesion. For example, several tests have shown thata smooth polyethylene sheet, bossed in a conventional way, reaches amaximum tear strength value of 0.15 N/mm², according to said standard.In fact, it is known that a smooth polyethylene sheet does not allow foran effective chemical adhesion, and furthermore the conventional shapeof the bosses, for example shaped as regular discs having a diameter of20 mm and a depth of 3 mm, does not form a sufficient mechanical grip;such a problem generally is the cause of the localised detachments,which sometimes occur in ceramic tile flooring or anyway in small-sizedcoverings.

Said UNI EN 1348 European standard of 2000 provides tensile tests onspecifically prepared reference samples. The adhesive is spread onto aconcrete plate by means of a putty knife equipped with 6×6 mm teeth andspaced apart by 12 mm from the centre, keeping an inclination of 60°;afterwards, said tiles are applied keeping on them a weight of 20 N for30 seconds. After the maturation of the adhesive, the tensile test iscarried out with a force of 200-300 N/s, connecting the tile to an axialtensile instrument by means of interconnection systems which do notentail bending efforts.

In case of interposition of said separating membrane, the preparation ofthe reference samples occurs by applying on a first bedding the membranesample being careful to exert such a pressure as to allow for a tightcoupling between the cement adhesive and the layer of nonwoven fabric,if present. Therefore, one spreads out the bedding again with a toothedputty knife for the application of the tile on the stickingsurface-being careful to fill the chambers of the bosses—which is thenpressed with a weight of 20N for 30 seconds. In particular, the bossedmembranes of the type provided by the invention have a substantiallysmooth plastic sheet, which does not simplify the connection neither tosaid cement adhesive nor to an optional layer of nonwoven fabric coupledwith it. The membranes, which are currently available on the market,reach much lower values with respect to the minimum initial adhesionvalue of 0.5 N/mm², a value greater than 0.2 N/mm² being alreadyconsidered as good.

Furthermore, it has been observed that in the specific sector offlooring there is no reference standard for assessing the adhesionbetween a plastic sheet and the base layer of fabric; to this purpose,it is possible to operate by measuring the delamination force with adynamometer. Substantially, one stresses the interface between saidfabric and the bossed sheet in such a way as to originate the reciprocaldetachment by delamination. In general, in the absence of regulationsintended to regulate this matter, in the case of composite materials onecan follow a test method prescribed for the delamination tests, whichare also called peel tests, such as the EN544 European standard, whichmeasures the so-called induced delamination. Such test provides tosample in different zones of the finished product some 10×20 cm samples,with the longer side facing the machine, and to stabilize the samplesfor 24 hours in laboratory, at 25° C. with 50% relative humidity. Froman operative point of view, one takes the fabric layer on one side andcarries out a delamination for a 10×10 cm area in such a way that thesample is half delaminated and half still adhering to the base fabric;afterwards, one inserts on the lower jaw of the dynamometer thedelaminated portion of the sheet while on the upper jaw, spaced by 20 cmfrom the lower jaw, one inserts the delaminated portion of the fabric.

In more detail as to the measurements, one carries out a traction of theso prepared product, which will be automatically delaminated by thedynamometer by means of the stroke of the upper jaw, which moves at afixed speed of 100 mm/min. The instrument measures the delaminationforce which will have a trend based on peaks, reaching the peak everytime the product is delaminated in correspondence of a row of bosses;said force, which is also defined as delamination force, is equal to thepeak value divided by the width of the sample, being thus expressed inN/mm. In particular, it has been observed that the membranes availableon the market generally have values of about 0.1 N/mm; such valuesexclusively refer to the systems coupled by thermal adhesion because itis known that the glued systems generally provide higher initial valuesbut in time, following the differences in temperature to which suchproducts are submitted during processing, the sticking tends to detach,sometimes giving rise to interruptions of the contact between theelements with the consequent lifting of the tiles.

Recently, the companies operating in the building sector have proposedseveral solutions of separating membranes, which are also intended toimprove the adhesion to the cement mortar by means of simplifiedgripping; in principle, one considers as conventional and advantageousthe bossed structures with undercuts as well, like localized fixingelements once the adhesive has hardened, and also one considers asconventional and advantageous the coupling of the sheet with a permeablelayer which penetrates the bedding. For example, among the mosteffective and widespread bossed membranes on the market we would like torecall the high-density polyethylene membrane solution by the Germancompany Schliiter-Systems KG—Iserlohn, www.schlueter.de—marketed underthe name of Ditra, which has bosses shaped as a 13 mm side square-plantruncated cone, arranged in a regular matrix with a 20 mm pitch, of thetype overturned in such a way as to obtain a dovetail section, or alsowe would like to recall the membrane solution by the Norwegian companyIsola AS-Porsgrunn, www.isola.no—marketed under the name of Platon,which has cylindrical bosses having a 13 mm diameter, arranged in aregular matrix with a 20 mm pitch, coupled with a fabric layer on bothfaces. However, it is widely known that such bossed membrane solutionshave said problems of initial adhesion or delamination; for example, theexperiments have shown that such solutions reach initial adhesionvalues, or pull-out values, included between 0.20 and 0.25 N/mm² withdelamination peak values of about 0.1 N/mm.

For the purpose of determining the prior art related to the proposedsolution, a conventional check was made, searching public archives,which has led to find some prior art documents, among which:

D1: US2006201092 (Saathoff et al.)

D2: US2011232217 (Hartl)

D3: EP2234802 (Becker)

D4: EP2246467 (Sghedoni)

D5: U.S. Pat. No. 7,536,835 (Schlueter)

D6: U.S. Pat. No. 6,434,901 (Schlueter)

D1 and D2 describe a membrane formed by a bossed sheet of the type withsimple protrusions shaped as a truncated cone facing downwards, that isto say, with the cavities facing upwards, which is coupled on the lowerside with a layer of nonwoven fabric and on the upper face with a net;in particular, in D said net is high-resistance and is stretched in aplanar way in such a way as to facilitate the penetration of the beddingmortar but hinder its tearing, after hardening, while in D2 said net iscoupled in adhesion with the upper face of the sheet for the purpose ofincreasing the adhesive effectiveness of the mortar by effect of theprojections formed by said net on the surface.

D3 proposes a separating membrane formed by a bossed sheet which iscoupled on both faces with a layer intended to improve the connection tothe cement adhesive, being for example of a synthetic material of thenonwoven fabric type.

D4 describes a separating membrane formed by a bossed sheet coupled onthe lower side with a layer of nonwoven fabric, wherein said sheet hastruncated cone bosses with cavities facing upwards and wherein the upperface of the sheet is entirely covered with fibres applied by gluing likein flocking. Said sheet is manufactured by rolling using a roller withregular protrusions with a truncated cone shape; said fibres, having alength between 500 and 1000 microns, are applied by spraying in a randommanner on the whole surface and on them one optionally applies apredetermined quantity of Teflon®, so as to prevent the capillarymovement of water.

D5 proposes a separating membrane comprising a bossed sheet havingundercuts, wherein the cavities of the bosses are facing downwards, thelower layer being permeable and being intended to be penetrated by theadhesive mortar from the screed in such a way as to remain gripped onthe dovetail undercuts present in some of them, whereas on the upperface said sheet is coupled with a second layer of nonwoven fabric whichacts as a planar support for the bedding mortar of the coating.Moreover, it is provided that the lower surface of the sheet hasimproved adhesion, being for example roughened or equipped with a roughcoating.

Finally, D6 describes a separating membrane comprising a bossed sheethaving undercuts, wherein the cavities of the bosses are facing upwardsto be filled by the adhesive mortar of the bedding applied over it andare equipped with protrusions which protrude horizontally from the edgeof the mouth towards the centre of each cavity, like a barrier, tohinder tearing once said mortar has hardened.

Therefore, it is reasonable to consider as known the solutions ofseparating membranes for building which are intended to separate thescreed from the coating, both said membrane and said coating being laidon an adhesive mortar bedding, which comprise:

-   -   a waterproof sheet of high-density polyethylene of the roller        bossed type in such a way as to form protrusions, generally of a        cylindrical, truncated cone or truncated pyramid shape with a        square base, which form cavities on the upper face into which        the bedding adhesive mortar can penetrate;    -   a permeable layer of nonwoven fabric which is coupled on one        side of said sheet for the purpose of joining the bedding in an        integral way;    -   means for increasing the adhesion of the adhesive mortar to the        sheet made by means of a net stretched or coupled in adhesion on        the whole surface of the face, or a fabric;    -   means for increasing the adhesion of the adhesive mortar to the        sheet, with mechanical gripping, made by means of undercuts        protruding from the mouth of the cavity or by means of a        high-resistance net stretched over them;    -   in principle, also known is the solution of improving the tear        strength of an adhesive to a polymer material in sheets or        plates by increasing roughness or wrinkledness, in such a way as        to increase the total area corresponding to the contact surface.

To conclude, we have observed that the known solutions described havesome drawbacks or anyway some limits.

In general, as described above, in the conventional and known solutionsit is possible to improve both the adhesion between the bossed sheet andthe overlying cement adhesive, and the adhesion between said bossedsheet and the underlying layer of nonwoven fabric.

Secondly, it has been observed that a net applied in a planar way on theupper face of the sheet, as for example in D1, effectively increasestear strength but also hinders the penetration of the adhesive mortarinto the cavities, with a high cost of the product and with greatercomplexity of application.

Thirdly, it has been observed that the solutions with fibres madeadherent to the sheet, such as the net of the conventional type as in D2or the particular flocking as in D4, realize micro-grips of the typeuniformly spread over the entire contact surface. However, it has beenobserved that in such cases production is not easy; in particular, forsaid flocked fibres one must first apply the adhesive, then spray thefibres and also, sometimes, apply a protective substance. Such a processis thus considerably longer and more expensive with respect to theconventional bossed membranes without said fibres on the upper face,also with greater costs of the materials and greater environmentalcosts. Furthermore, the known solutions in principle provide that thelower surface of the sheet has improved adhesion, as for example in D5,where it is generically proposed to obtain said improvement by means ofa roughened surface or a surface with a rough coating; to this purpose,however, it is not described and it is not known how to industriallyrealize said roughening on the smooth surface of a bossed membrane, andparticularly in order to obtain an effective adhesion to the adhesive,with low costs and for large production volumes.

Fourthly, in the known solutions of bossed sheet also with undercuts inthe cavities, as for example in D5 and D6, it has been observed that themanufacturing process for obtaining them is not easy, since theprocessing cycle is longer and more complex with greater waste and alsowith greater investments in the equipment. The experiments have shownthat, for the purpose of gripping, the protrusions constituting saidundercuts are generally placed on the edge of the chamber, at the mouth,like a necking which effectively hinders the extraction of the adhesiveonce it has hardened but which also hinders its entry, during laying;such a configuration in professional use requires time and attention inorder to prevent the incomplete filling of the chambers. Therefore, tothis purpose it has been observed that a lower positioned protrusion,with respect to the mouth, is more effective, in such a way as to createa sort of guide for the adhesive to enter the chamber and facilitate thecomplete filling under the necking; moreover it has been observed that,for the purpose of gripping, a thin section of the restraint below saidnecking is sufficient, with a lower quantity of material to beintroduced, while the addition of said guide at the mouth above saidnecking effectively contributes to increasing the contact surface and,as a consequence, the gripping.

Furthermore, it has been observed in the solutions of bossed sheetcoupled with a layer of nonwoven fabric that the latter adheres to thecement' adhesive also having said delamination problems and that suchproblems are reduced by increasing the contact surface with the fabricand increase by decreasing said contact surface. Thus, the experimentshave shown that the most widespread solutions on the market have acontact area in a percentage with respect to the whole face of themembrane and corresponding to the heads of the bosses joined to thefabric which is generally between 33% and 49% of the total face; suchvalues are reported respectively to said solutions with square bosseshaving a 13 mm side and with circular bosses having a 13 mm diameter,with a 20 mm pitch, respectively. Furthermore, it has been observed thatit is not advantageous to increase said contact area too much becausethis increases said delamination values but causes a worsening of saidvalues of initial adhesion on the opposite face; to this purpose, theexperiments have shown that, on the other hand, it would be excellent tohave a percentage of area of contact with the fabric, that is to say,corresponding to the heads of the bosses on the lower side, which isabout between 50% and 75% of the total area of the face.

Hence the need for the companies of the sector to find solutions whichare more effective with respect to the existing solutions; the aim ofthe present invention is also to solve the described drawbacks.

BRIEF SUMMARY OF THE INVENTION

This and other aims are achieved by the present invention according tothe characteristics as in the appended claims, solving the arisingproblems by means of a separating membrane (10) of plastic material,made up of a bossed and waterproof sheet (100) which is coupled with apermeable base layer (101); the bosses (102) are of the cylindrical typewith a double diameter (D1, D2), and have such a structure andarrangement as to have an improved adhesion on both faces (110-111). Theinvention increases the gripping of the adhesive for a greater tearstrength, on the upper face, and at the same time increases the area ofcontact with the base layer for a greater resistance to delamination onthe lower side. In particular, inside each chamber (103) there is aninternal crown (104) which divides it like a necking (D2) into twosuperimposed compartments (105-6) of identical diameter (D1), whereinthe first compartment has a depth (HI) equal to at least ⅓ of the total(H). The invention also relates to a production process for obtainingsaid membrane (10).

In this way, by the considerable creative contribution the effect ofwhich constitutes an immediate technical progress, various advantagesare achieved.

A first aim consists in realizing a separating membrane, of the bossedtype, which at the same time is intended to improve both the adhesion onthe lower face, for the purpose of a greater resistance to saiddelamination, and the gripping on the upper face, to increase saidinitial adhesion to the cement adhesive with respect to the conventionalsolutions.

A second aim consists in realizing a separating membrane with restraintelements of the type forming a necking which at the same time simplifythe laying and the uniform filling of the cement adhesive inside thechambers, also under the necking, and make the gripping wider and moreeffective.

A third aim consists in realizing a membrane equipped with bosses havinga particular structure for facilitating laying and at the same timeimproving adhesion, which are formed with extreme precision.

A fourth aim consists in realizing a membrane easy to be manufactured inan industrial plant with high production volumes, which is considerablymore economical than the known and conventional solutions.

These and other advantages will appear from the following detaileddescription of some preferred embodiments with the aid of the schematicdrawings enclosed, whose details of execution are not to be consideredlimitative but only illustrative.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1 a-c show a conventional membrane of plastic material withcylindrical bosses arranged with a regular pitch, also being coupled onthe lower side with a base layer of nonwoven fabric, according to theprior art; in particular, FIG. 1 a is an axonometric view of a portionof said membrane, FIG. 1 b is a plan view, FIG. 1 c is a detail sectionon the section plane XI-XI of FIG. 1 b.

FIG. 2 shows a plan view of a portion of the separating membraneaccording to the invention, with undercut protrusions inside the chamberwhich are shaped as an internal crown.

FIG. 3 a is a detail section on the section plane X2-X2 of FIG. 2 , in afirst variant in which the internal crown has flattened edges; FIG. 3 bis an enlargement relating to said internal crown, of FIG. 3 a.

FIG. 4 a is a detail section on the section plane X2-X2 of FIG. 2 , in asecond variant in which the internal crown has the lower edge inclined;FIG. 4 b is an enlargement relating to said internal crown, of FIG. 3 a.

FIGS. 5 a-d show plan views of portions of separating membrane, of FIG.2 , in different configuration variants of the bosses in particularreferring to a base configuration (FIG. 5 a ) with individually alignedcylindrical bosses with constant pitch, or even double (FIG. 5 b ),triple (FIG. 5 c ) or combined (FIG. 5 d ) and keeping the same positionas said base configuration, the dotted perimeters of the cylindricalbosses being superimposed to facilitate understanding.

FIGS. 6 a-d show plan views of the membrane portion of FIGS. 5 a-b inwhich the contact surface between the head of the boss and the baselayer is represented in contrast with respect to the non-adherentsurface.

FIG. 7 a shows a detail section of the membrane formed around the bossedforming roller, it being referred to the variant of FIG. 3 a ; FIG. 7 bis an enlargement relating to the profile of the single boss.

FIG. 8 a shows a detail section of the membrane formed around the bossedforming roller, it being referred to the variant of FIG. 4 a ; FIG. 8 bis an enlargement relating to the profile of the single boss.

FIG. 9 is a simplified diagram of the process for roughening a bossedmembrane, according to the present invention, depending on theconfiguration of the roughening.

FIGS. 10 a-b, 11 a-b and 12 a-b schematically show a bossed membrane inthe roughened version, according to the present invention. Inparticular, FIG. 10 a is an axonometric view of the roughened membranein a first variant with porous surface, FIG. 10 b being a detail sectionof FIG. 10 a ; FIG. 11 a is an axonometric view of the roughenedmembrane in a second variant with cut surface, FIG. 11 b being a detailsection of FIG. 11 a ; FIG. 12 a is an axonometric view of the roughenedmembrane in a third variant with combined porous and cut surface, FIG.12 b being a detail section of FIG. 12 a.

FIGS. 13 a-b indicatively show enlarged orthogonal views, respectivelyfrom the top and in section X3-X3, being referred to a portion having a3×3 mm width of the roughening porous surface as in FIGS. 10 a-b , in afirst variant with superficial microcavities in the form of singlemicropores.

FIGS. 14 a-b indicatively show enlarged orthogonal views, respectivelyfrom the top and in section X4-X4, being referred to a portion having a3×3 mm width of the roughening porous surface as in FIGS. 10 a-b , in asecond variant with superficial microcavities in the form of compositepores.

FIGS. 15 a-b indicatively show enlarged orthogonal views, respectivelyfrom the top and in section X5-X5, being referred to a portion having a3×3 mm width of the roughening cut surface as in FIGS. 11 a-b , in afirst variant with superficial brushing microcavities in the form ofdiscontinuous grooves.

FIGS. 16 a-b indicatively show enlarged orthogonal views, respectivelyfrom the top and in section X6-X6, being referred to a portion having a3×3 mm width of the roughening cut surface as in FIGS. 11 a-b , in asecond variant with superficial grinding microcavities in the form oflinear, elongate and parallel grooves, in oriented bundles.

DETAILED DESCRIPTION OF THE INVENTION

With reference also to the Figures (FIGS. 2-8 ), the invention relatesto a separating membrane (10) for building and to the industrial processfor obtaining it. The structure of the membrane is of the known andconventional type, it being originated from an extruded sheet (100) ofplastic material and provided with bosses (102) arranged in a matrixwith a regular pitch (P), which protrude from the lower face (111) tolean on the load-bearing structure and allow the bedding layer appliedon the upper face (110) to penetrate the related chambers (103), it alsobeing coupled on the lower side, according to the prior art, with a baselayer (101) of nonwoven fabric for the purpose of realizing amulti-layer membrane of the separating type. In particular, the membrane(10) provided by the invention has bosses (102-3) having a particularshape and a particular arrangement, in such a way as to have improvedadhesion on both faces (110-1), thus increasing the gripping of thecement adhesive for a greater tear strength and, at the same time,increasing the contact area with the base layer for a greater resistanceto delamination.

The invention provides a bossed sheet (100, 102-3) of a plastic materialsuch as polyethylene, polypropylene or a mixture thereof; said baselayer (101) is preferably of a nonwoven polypropylene fabric, of thetype called spunbonded or spunlace. The thickness of the extruded sheetis directly proportional to its weight, which may range from 350 to 1000g/m²; in particular, it has been observed that to a weight of 0.9 g/m²corresponds more or less a thickness of 1 micrometre, therefore in thecase of the preferred but not limitative configuration of extrudedproduct of 500 g/m² in weight corresponds a thickness of about 550micrometres. The total thickness (SI) of the bossed sheet (100),including the protruding bosses and the thickness of the sheet itself,is preferably of 3 mm; however, in case of particular applications itcan be greater, being for example of 5 mm and up to 7 mm.

In more detail as to the particular restraint element for the adhesiveof the cement type, the invention (FIGS. 2, 3 a-b, 4 a-b) provides thatthe chambers (103), obtained on the upper face (110) from the bosses(102) are equipped with an internal crown (104), having a constant width(L) of at least 0.8 mm, and preferably 1 mm, which acts as an undercutrestraint element and which divides like a necking (D2) the internalspace of the chamber (103, H) into at least two compartments (105-6).The first compartment (105) is cylindrical, has a diameter (D1) of 20mm, a depth (HI) between ⅓ and ½ of the total depth (H) of the chamber(103) for the purpose of facilitating the entry of the cement adhesiveand facilitate the complete filling of the chamber (103, 105-6), actingas a funnel, and increasing the contact surface; the second compartment(106) is formed by the necking (D2) in correspondence of said internalcrown (104) and by the underlying and cylindrical (D1) widening (107)which simplifies restraint for the hardened adhesive, with a depth (H2)complementary to (HI) which is between ½ and ⅔ of said total depth (H).Said widening (107) having a depth (H3) at least equal to ⅙ of saidtotal depth (H). All the above-indicated values being considered with atolerance of +/−10%.

In particular, said internal crown (104) is made during the bossing ofthe extruded sheet, as described in the following, forcing it into eachprotrusion (201 a-b) of the forming roller (200), which is laterallyprovided with notches (203) in such a way as to obtain two folded edgesjoined to each other which protrude towards the inside of the chamber(103). In a first variant (10 a), said internal crown has flattenededges (108-9), that is to say pressed in a parallel way one on top ofthe other in a substantially orthogonal direction with respect to theside walls of the chamber (FIGS. 3 a-b, 7 a-b ); in a second variant (10b), said internal crown has the lower edge (109) inclined by 45° withrespect to the upper edge (108), leaving said underlying widening (107,D1) with a depth (H3) at least equal to ⅙ of said total depth (H), asdescribed above (FIGS. 4 a-b, 8 a-b ). All the above-mentioned valuesbeing considered with a tolerance of +/−10%.

In more detail as to the overall increase in the contact surface (112)with the base layer (101) stretched below said sheet (100), it isobserved that said bosses are of the cylindrical type, with a greaterdiameter (D1) of 20 mm and arranged in a matrix with a constant pitch(P) of 26 mm; such values being considered with a tolerance of +/−10%.In this way one obtains a contact area (112) between the sheet (100) andthe base layer (101), in correspondence of the heads of the bosses,which is larger with respect to the known and conventionalconfigurations, being at least equal to 50% of the total area of theface. For the purposes of the invention, in particular, it is providedthat said contact area is between 50% and 75% of the total area of theface, wherein such values are obtained by varying said baseconfiguration (114 a) (FIG. 5 a ), having individually alignedcylindrical bosses, that is to say, being grouped in groups of two (114b) (FIG. 5 b ), three (114 c) (FIG. 5 c ) or combined (114 d) (FIG. 5 d) single and grouped, although always maintaining the same setting assaid base configuration. Set out below are some application examples.

In a first application example, corresponding to the base configurationof the invention (10) (FIG. 2, 5 a), there are provided bosses (102-3)of the cylindrical type with a double diameter (D1, D2) the externalcylinder (D1) comprising said internal crown (104, D2) which subdividesthe chamber (103) into the two above-described compartments (105-6).Preferably, the bossed sheet (100) is of HDPE with a total thickness(SI) of about 3 mm, with a greater diameter (D1) of the bosses of 20 mmand with a pitch (P) of 26 mm; said sheet also being thermocoupled witha base layer (101) of nonwoven polypropylene fabric and with a contactarea amounting to 50% of the whole face. Said internal crown (104) can,preferably but not exclusively, be made in said two variants (10 a-b) asdescribed in the following.

As a non-exhaustive example, in a first variant of the bossing (10 a)said first compartment (105) has a depth (HI) equal to ⅓ of the total(H), said second compartment (106) has a depth (H2) equal to ⅔ of thetotal and includes the widening (107) having a depth (H3) equal to aboutone third of the total; in this way one has experimentally obtained avalue of resistance to the delamination between the base layer and thesheet of 0.30 n/mm, and one has also obtained a value of initialadhesion with the cement adhesive of 0.25 N/mm². Furthermore, in asecond variant (10 b) said first compartment has a depth (HI) equal to ½of the total (H), said second compartment has a depth (H2) equal to ½ ofthe total with the widening (107) having a depth (H3) equal to about ⅙of the total; in this way one has equally obtained a value of resistanceto said delamination of 0.30 n/mm, and one has also obtained a value ofsaid initial adhesion of 0.25 N/mm².

In an embodiment variant (114 b) with respect to said base configuration(114 a) (FIGS. 5 b, 6 a ), it is provided to group two adjacentcylindrical bosses, that is to say, to replace the single bosses withpairs in the form of elongate bosses of the oval type, two by two and inthe same position. Calculating the area corresponding to the head ofsaid grouped bosses, one obtains in percentage a contact surface (112)increased from 50% to 66% with respect to the total area.

In another embodiment variant (114 c) (FIGS. 5 c, 6 b ), it is providedto group three adjacent cylindrical bosses, that is to say, to replacethe single bosses with triple groups in the form of further elongatebosses of the oval type, three by three and in the same position.Calculating the area corresponding to the head of said grouped bosses,one obtains in percentage a contact surface increased to 72% withrespect to the total area.

In a further embodiment variant (114 d) (FIGS. 5 d, 6 c-d ), it isprovided to combine said configurations of grouped bosses, double ortriple, alternating them with single bosses and in the same position. Bythis solution one advantageously obtains a value of said resistance todelamination of 0.40 n/mm, and one also obtains a value of said initialadhesion of 0.35 N/mm².

In another variant of the invention, in order to further increaseadhesion, it is provided to roughen at least one face of said bossedsheet by means of superficial microcavities, which are open towards theoutside of the surface in such a way as to allow for a gripping of thewidespread type and realizing at least one of the following rougheningconfigurations of the membrane: with porous or cut surface.

The process for industrially obtaining the above-described separatingmembrane includes the following operating phases: extruding the rawmaterial in such a way as to form a thin sheet (100), said raw materialconsisting of at least one thermoplastic polymer or a mixture ofpolymers; then forming said sheet around a forming roller (200) of thebossed type, that is to say, being provided with protrusions (201)arranged in a matrix with a constant pitch (P) and a height between 2.5mm and 7 mm, and preferably in such a way as to obtain a total thicknessof the sheet (SI) of 3 mm; at the end of the forming, coupling on thelower side (111) of said sheet (100) the base layer (101) of nonwovenfabric, of the type called spunbonded. The invention, for the purpose ofobtaining said bosses (102) of the cylindrical type with a doublediameter (D1, D2) which also include the particular above-describedinternal crown (104, L), provides that each protrusion (201) of theroller (200) laterally comprises a main notch (202), shaped as acontinuous cavity and orthogonal to the side walls of the boss, which isintended to fold the sheet (100) forcing its forming in such a way as torealize two folded edges (108, 109), undercut-joined, which protrudetowards the inside of the chamber (103) in said first variant (10 a) orin said second variant (10 b) of configuration of said internal crown(104). Said main notch preferably having a width (L) of 1 mm and aheight at least equal to twice the thickness of the sheet.

In a first embodiment variant of the protrusion (201 a) said main notch(202 a) is configured with a rectangular section, in such a way as toform said internal crown (104) with the edges (108-9) flattened one ontop of the other, that is to say, pressed in a horizontal direction andnamely substantially parallel to the external surface of the roller(FIGS. 3 a-b, 7 a-b ).

In a second embodiment variant (200 b) said main notch (202 b) isconfigured with a triangular section with the lower face inclined by45°, in such a way as to form an internal crown (104) with the loweredge (109) inclined by 45° with respect to the upper edge (108), whichis substantially parallel to said roller (FIGS. 4 a-b, 8 a-b ).

Preferably, each protrusion (201) of the roller also has a secondarynotch (203), shaped as a thin and continuous cavity, placed laterally atthe base of the protrusion, which substantially reduces the portion ofconnection of the protrusion to the roller. Said secondary notch isintended to facilitate the forming operations at the base of the boss(102) allowing the sheet (100) to adapt itself to forming, by deformingand expanding.

Said notches (202-3) subdivide the protrusion (201) into four mainportions (204-7) (FIGS. 3 a-b, 4 a-b, 7 a-b, 8 a-b ):

-   -   a first portion (204) is cylindrical and is in correspondence of        the secondary notch (203);    -   a second portion (205) is cylindrical and corresponds to the        greater diameter (D1) of the boss (102); said first and second        portion (204-5) forming said upper compartment of the boss (102,        HI);    -   a third portion (206) is alternatively cylindrical (206 a, D2)        or shaped as a truncated cone (206 b) and is in correspondence        of said primary notch (202) to form respectively said internal        crown in the two above-described embodiment variants (104 a-b);    -   a fourth portion (207) is cylindrical (D1) and corresponds to        the greater diameter (D1) of the boss on the widening (107, H3)        underlying said internal crown (104); said third and fourth        portion (206-7) forming said lower compartment of the boss (106,        H2).

In more detail as to said four main portions:

-   -   said first portion is cylindrical, has a diameter between 13 mm        and 18 mm and a height of 0.5 mm;    -   said second portion is cylindrical, has a diameter of 20 mm and        a height between 0.5 mm and a maximum height equal to ½ of the        total height;    -   said third portion is alternatively cylindrical, with a diameter        18 mm and a height equal to twice the thickness of the sheet        (100), or is shaped as a truncated cone with an inclination of        45° starting from 18 mm up to 20 mm towards said fourth portion;    -   said fourth portion is cylindrical, has a diameter of 20 mm and        a maximum height equal to ⅙ of the total height of the        protrusion.

Furthermore, the industrial process (30 a-c) for obtaining a roughenedmembrane is described, said process being suitable for any bossedmembrane (40 a, 40 b, 40 c) (FIGS. 10-16 ) consisting of an extrudedsheet of plastic material and formed around a bossed roller equipment,and being particularly suitable for the separating membrane (10 a, 10 b)described above (FIGS. 2-8 ), that is to say, according to theinvention; it must be noted that said process (30 a-c) can also be usedto roughen any configuration of bossed membrane in correspondence of atleast one face of the plastic sheet. With reference also to theschematic figures (FIGS. 9-16 ), enclosed for illustrative purposesonly, said process (30 a-c) allows to advantageously obtain a roughenedmembrane (10 a-b, 40 a-c) comprising particular roughening superficialmicrocavities (411 a-d) which are open outwards in such a way as torealize a micro-gripping of the widespread type, for example tofacilitate the adhesion of a cement adhesive; said superficialmicrocavities, having a depth greater than 35 micrometres, form one ofthe following roughening configurations: with porous surface (40 a, 401)(FIGS. 10 a-b ), with cut surface (40 b, 402) (FIGS. 11 a-b ) or withcombined surface (40 c, 401-2) (FIGS. 12 a-b ).

In said first configuration (FIGS. 10 a-b ), the roughening of themembrane (40 a) occurs with a porous surface (401) wherein themicrocavities are of the type with pores (411 a-b) formed by the bubblesof the gas which is advantageously contained in the materialconstituting the sheet and which comes out in a controlled way duringthe production phases in such a way as to leave in the material somegaps shaped as craters (412-3) and distributed in a random way, with ahomogenous distribution density, over the entire surface of the face andalso in the chambers (406). In said second configuration (FIGS. 11 a-b )the roughening of the membrane (40 b) occurs with a cut surface (402)wherein the microcavities are of the type with cuts (411 c-d)mechanically obtained in correspondence of the portions ofnon-protruding surface of the roughened face, that is to say, on themost external surface and not inside the chambers and namely on thenon-bossed parts of the sheet. In said third configuration (FIGS. 12 a-b) the roughening of the membrane (40 c) occurs with a combined surface(401-2) where there are simultaneously both said porous surface (401)and said cut surface (402); in that case, said microcavities with cuts(411 c-d) are mechanically made on a surface which already comprisessaid microcavities with pores (411 a-b).

Said process (30 a-c) in short provides the following operating phases:extruding the raw material in such a way as to form a sheet (400), saidraw material consisting of at least one thermoplastic material or amixture of polymers; then forming said sheet (400) around a bossedroller equipment provided with protrusions arranged in a regular matrixin such a way as to form a membrane with bosses (405); optionallyrealizing the coupling of a nonwoven fabric, on the face where theroughening is not provided; and wherein in particular the processprovides, depending on each of said roughening configurations (40 a-c)(FIG. 9 ):

-   -   to obtain said first roughening configuration (40 a), the        process (30 a) provides to join to the plastic material, before        extrusion, an additive producing some gas which comes out during        the forming phase, said additive being alternatively a mineral        filler or a foaming agent;    -   to obtain said second roughening configuration (40 b), the        process (30 b) provides that, after the forming around the        bossed roller, the bossed sheet crosses some thermal        conditioning rollers where there are also some driving means        which force it to pass on a working surface under rotating means        which are intended to cut it mechanically, said rotating means        being alternatively of the type for brushing or grinding;    -   to obtain said third roughening configuration (40 c), the        process (30 c) provides to combine said processes (30 a-b)        realizing mechanically said microcavities of the type with cuts        (402 a-b, 411 c-d, 40 b) on a surface which already comprises        said microcavities with pores (401 a-b, 411 a-b, 40 a).

In more detail as to the carrying out of the process (30 a) forobtaining said first configuration (40 a), with porous rougheningsurface (401), it is provided:

-   -   in a first variant (401 a) (FIGS. 13 a-b ), to add to the        plastic material some particles of mineral filler of nanometric        dimensions where 99% of the particles have a diameter smaller        than 50 micrometres, in a quantity between 1% and 20% of the        total raw material, and with a humidity lower than 0.5%; wherein        said mineral filler is calcium carbonate;    -   in a second variant (401 b) (FIGS. 14 a-b ), to add to the        plastic material a quantity of foaming agent between 0.25% and        2% of the total mixture of raw material, said foaming agent        being compatibilized with said plastic matrix in such a way that        at the moment of extrusion it reacts with the atmosphere; and        wherein said quantity of foaming agent forms a roughened        membrane of the waterproof type; wherein said foaming agent        alternatively is: of the type azodicarbamide in polyethylene        matrix at 0.5% in weight on extrusion of HDPE at 500 g/m², or of        the type Hostatron AEL 601 in polyethylene matrix at 1.5% in        weight on extrusion of HDPE at 600 g/m²;    -   in a further variant with respect to the previous one, to add to        the plastic material a quantity of foaming agent between 2% and        5% of the total mixture of raw material in such a way as to form        a roughened membrane of the permeable and microperforated type;        wherein said foaming agent is alternatively of the type        Hostatron AEL 601 in polyethylene matrix at 2.5% in weight on        extrusion of HDPE at 600 g/m².

In more detail as to the carrying out of the process (30 b) forobtaining said second configuration (40 b), with cut roughening surface(402), it is provided:

-   -   in a first variant (402 a) (FIGS. 15 a-b ) said rotating means        are intended for brushing being of the type with a rotating        shaft covered with metal brushes which act in such a way as to        cut it forming said microcavities in the form of discontinuous        grooves (411 c); wherein the mouth (415) of said discontinuous        grooves (411 c) has a mainly circular and/or ovalized and/or        irregularly polygonal shape, a depth (V2) between 35 micrometres        and 200 micrometres and a width (VI) which is between 1 mm and 2        mm if measured on the diagonal in the brushing direction, and is        between 0.5 mm and 1 mm if measured on the diagonal in a        direction perpendicular to it; wherein said shaft is provided        with said brushes over its entire width and wherein the metal        bristles which make them up are spaced 2.5 mm to 5 mm from one        another, with a rotational speed of the shaft higher than 1000        revolutions/minute, while the product advances at linear speeds        of 3 metres/minute; wherein the removed chip (416) of each of        said microcavities (411 c) obtained by brushing can        alternatively be left, that is to say, it is joined to the mouth        (415) in a protruding way to increase the wrinkledness of the        surface, or can be removed;    -   in a second variant (402 b) (FIGS. 16 a-b ) said rotating means        are intended for grinding being of the belt grinder type        arranged in series in such a way as to cut said sheet for a        depth (V2) smaller than 100 micrometres, forming multiple        microcavities (411 d) mainly in the form of elongate grooves,        oriented in at least two different directions to form a net-like        geometry, wherein the pitch (V4) between two successive and        parallel grooves is between 0.1 mm and 0.2 mm and the angle (β)        between a primary direction (417 a) and a secondary direction        (417 b) is between 15° and 90°.

In more detail as to said porous surface (401) made by theabove-described process, the first version (401 a) features superficialmicrocavities (411 a) shaped as single micropores having the crater(412) with the mouth (415) of a mainly circular shape, a width (VI)smaller than 200 micrometres and a depth (P) smaller than 95micrometres; said superficial microcavities (411 a) realizing aroughened membrane with a porous appearance of the waterproof type(FIGS. 13 a-b ).

Moreover, in the second version (401 b), said porous surface comprisessuperficial microcavities (411 b) shaped as composite pores, withcraters of the single type (412) and of the multiple type (413) as well;and wherein said craters of the multiple type (413) comprise at leasttwo sub-craters (414 a-b) joined to each other, being intersected and/orincorporated; and wherein said craters of the multiple type (413) have awidth (VI) smaller than 300 micrometres and a depth (V2) which isvariable depending on the type and on the quantity of the gas which hascome out of the material and which is also variable depending on theproduction modes; and wherein said superficial microcavities (411 b)realize a roughened membrane with a porous appearance which is of thewaterproof type, if said depth (V2) is smaller than the thickness (V3)of the sheet, or is of the permeable and microperforated type if theyare pass-through, that is to say, open on the lower face (410) as well(FIGS. 14 a-b ).

In more detail as to said cut surface (402) made by the above-describedprocess, in a first version (402 a) it comprises superficialmicrocavities (411 c) which are made mechanically by brushing, whereinsaid superficial microcavities (411 c) are shaped as discontinuousgrooves, with the mouth (415) having a mainly circular and/or ovalizedand/or irregularly polygonal shape, a depth (V2) between 50 micrometresand 200 micrometres and a width (VI) between 0.5 mm and 2 mm; saidsuperficial microcavities (411 c) realizing a roughened membrane (40 c)of the waterproof type with a wrinkled appearance. Furthermore, it isprovided that said superficial microcavities (411 c) can have on theoutside the related removed chip (416), which remains joined to thesurface in correspondence of the mouth (415) without being removedcompletely; in this case, therefore, one obtains a roughened membrane ofthe waterproof type with a wrinkled appearance with an improved gripping(FIGS. 15 a-b ) as well.

Moreover, in a second version (402 b), said cut surface comprisessuperficial microcavities (411 d) shaped as linear, elongate andoriented grooves, assimilable to continuous grooves, which are mademechanically by grinding; the superficial microcavities (411 d) aredistributed in a regular way being parallel and grouped in bundles (418a-b), said bundles (418 a) being oriented at least according to aprimary grinding direction (417 a) and also intersected by other bundles(418 b) according to a secondary direction (417 b) which cuts throughsaid primary direction (417 a) with a relative angle (a) which isbetween 15° and 90°. The depth (V2) of said superficial microcavities(411 d) is between 100 micrometres and 500 micrometres; the pitch (V4)between two parallel and successive microcavities (411 d) of the bundle(418 a-b) is between 0.1 mm and 0.2 mm. Said superficial microcavities(411 d) realize a roughened membrane of the waterproof type with awrinkled appearance (FIGS. 16 a-b ).

In particular, it is observed that said superficial microcavities of thetype with cuts (402, 411 c-d) are made mechanically in correspondence ofthe external surfaces and come into contact with the cutting equipment,that is to say, in correspondence of the non-extruded portions ofsurface of the face outside the chambers (406) (FIGS. 11 a-b ).

In an alternative configuration, it is provided that said superficialmicrocavities (411 a-d) are made both on the upper face (409) and on thelower face (410) of the sheet (400). In case of combined porous and cutsurfaces, in particular, it is observed that on the lower face saidsuperficial microcavities of the type with cuts (411 c-d) are made onlyin correspondence of the heads (408) of said bosses (405), that is tosay, on the surfaces which come into contact with the cutting equipment.

Furthermore, as to said porous surface (401) made by the above-describedprocess, it is observed that said microcavities (411) of the type withpores (411 a-b) are formed by the bubbles of a gas which is contained inthe material of the sheet and has come out in a controlled way duringthe production process, leaving in the material some gaps shaped assmall craters (412-3) and distributed in a random way with homogenousdensity over the entire surface of the face (409) and also inside thechambers (406) (FIGS. 10 a-b ). To this purpose, in the first variant(401 a) of roughening with pores where said superficial microcavities(411 a) are shaped as micropores (FIGS. 13 a-b ), it is provided to usein the raw material some mineral additives, which are also calledmineral fillers, preferably calcium carbonate; in fact, experiments haveshown that the use of a mineral filler leads, in the operatingconditions provided by the invention, to a roughened surface withsmall-sized pores having a generally circular area. In the secondvariant (401 b) of roughening with pores, on the other hand, where saidsuperficial microcavities (411 b) are shaped as composite pores withcraters of the single type (412) and also of the multiple type (413), itis provided to use in the raw material some foaming agents; in fact,experiments have shown that the use of a foaming agent leads, in theoperating conditions provided by the invention, to a roughened surfacewith larger-sized composite pores with respect to the micropores of theprevious variant, both with reference to the area and to the depth (V2)of each crater, also being joined to form sub-craters (414 a-b).Furthermore, it has been observed that, if said sub-craters are numerousand joined to each other inside the same microcavity, the related crater(413) has on the inside a foam-like structure of the material.

In more detail as to said first variant (401 a) of roughening with pores(FIGS. 13 a-b ), it is provided to add to the plastic material someparticles of mineral filler, preferably calcium carbonate, of nanometricdimensions, that is to say, with 99% of the particles having a diametersmaller than 50 micrometres, and being in a quantity between 1% and 20%of the total raw material, and also being with low humidity, that is tosay, lower than 0.5%. In particular, it has been observed that, upongrowing of the quantity of said mineral filler up to a maximum of 20% onthe total raw material, one obtains superficial pores with a growingdiameter, that is to say, up to 200 micrometres, and a depth (V2) up to50 microns; substantially said superficial pores are formed because ofthe relative humidity present in the calcium carbonate. This phenomenoncan be advantageously used for the purposes of the invention by notdegassing the melted material during extrusion but allowing, and at themoment of the casting from the extrusion head, the gas microbubbles tospread out in a homogenous way in correspondence of the surface of theroller, to then come out naturally leaving on the entire hardenedsurface of the membrane the respective microcavities, in the form ofmicropores.

In more detail as to said second variant (401 b) of roughening withpores (FIGS. 14 a-b ), it is provided to insert in the mixture ofplastic materials in extrusion, a foaming agent, compatibilized with theplastic matrix, which at the moment of extrusion reacts with theatmosphere. In general, one can consider as known various foamingsubstances, organic or inorganic, which are used to produce low-densitypolymer products; such substances, once the reaction temperature hasbeen reached, expand in an exothermic and irreversible way, releasing agas which generates in the products of plastic material a foam-likestructure.

For the purposes of the invention, in particular, experiments have shownthat by applying such a foaming system directly in the extrusion withflat head for membranes, that is to say, by adding to the mixture of theraw materials a quantity of foaming agent between 0.25% and 2% of thetotal raw material, one obtains an extruded waterproof sheet of therough type, characterised by the presence of microcavities whose volumeand concentration are directly proportional to the percentage of foamingagent used. It has also been observed that, if dosed in greaterquantities, the foaming agent may lead to the production of an extrudedpermeable sheet in which the cavities created by the expansion arepass-through; in fact, an addition between 2% and 5% allows to obtain amicroperforated extruded sheet which is effective as a separatingmembrane for internal use, or even for external use if the stratigraphyprovides the insertion of a drainage and waterproofing element under thescreed.

In a first production example of said second variant (401 b) ofroughening with pores, particularly suitable for the invention is afoaming agent of the type azodicarbamide in polyethylene matrix, at 0.5%in weight, on extrusion of HDPE at 500 g/m²; the so extruded membrane isno longer smooth but has a roughness extending over the entire surfaceof the face, and wherein each microcavity mainly has a diameter smallerthan 100 micrometres and a depth (V2) smaller than 50 micrometres. In asecond production example of said second variant (401 b) of rougheningwith pores, particularly suitable for the invention is a foaming agentof the type called Hostatron AEL 601 in polyethylene matrix, at 1.5% inweight, on extrusion of HDPE at 600 g/m2; the so extruded membrane is nolonger smooth but has a roughness extending over the entire surface ofthe face, and wherein each microcavity mainly has a diameter rangingbetween 200 and 400 microns and a depth (V2) smaller than 50micrometres. In a third production example, particularly suitable forthe invention is a foaming agent of the type called Hostatron AEL 601 inpolyethylene matrix, at 2.5% in weight, on extrusion of HDPE at 600g/m²; the extruded membrane is no longer continuous but is perforatedthanks to the formation of pass-through cavities having a diametergreater than 500 microns.

Furthermore, as to said cut surface (402), it is observed that saidsuperficial microcavities are obtained by means of a mechanical actionand not an action of the chemical-physical type, as occurs for saidporous surface (401), and it is also observed that the action concernsonly the most external portion of the sheet, that is to say, thenon-bossed part, cutting only the surface in direct contact with thecutting equipment and not that inside the chambers (406). To thispurpose, in a first variant (402 a), by means of brushing one creates byremoval some superficial microcavities in the form of discontinuousgrooves; in a second variant (402 b), by means of grinding one createsby removal some superficial microcavities in the form of linear,elongate and parallel grooves, in oriented bundles, assimilable tocontinuous grooves.

In more detail as to said first variant (402 a) of roughening bybrushing (FIGS. 15 a-b ), once extruded and if necessary coupled with anonwoven fabric, said sheet passes through some thermal conditioningrollers; between said rollers there is a driving system which guides theproduct to pass under a shaft covered with metal brushes: in fact, ithas been observed that the rotation of said brushes creates on thesurface of the sheet said microcavities in the form of discontinuousgrooves (411 c). In an advantageous production configuration, using ashaft provided with said brushes over its entire width and wherein themetal bristles which make them up are spaced 2.5 mm to 5 mm from eachother, with a rotational speed of the shaft greater than 1000revolutions/minute, while the product advances at a linear speed of 3metres/minute, irregularly shaped grooves are formed, affecting areashaving a length between 1 mm and 2 mm and a width between 0.1 mm and 0.5mm, the dimensions being greater in the brushing direction. Such aconfiguration allows to obtain discontinuous grooves with the mouth(415) having a mainly circular and/or ovalized and/or irregularlypolygonal shape, a depth (V2) between 50 micrometres and 200 micrometresand a width (VI) which is between 1 mm and 2 mm if measured on thediagonal in the brushing direction, and which is between 0.5 mm and 1 mmif measured on the diagonal in a direction perpendicular to it; suchgrooves can still be connected to the removed chip or not.

In more detail as to said second variant (402 b) of roughening bygrinding (FIGS. 16 a-b ), which is also called lapping, instead of saidshaft covered with metal brushes there is a series of belt grinderswhich act on a working surface through which the product is sent, beingpulled by a drive; in particular, such grinders operate in such a way asto obtain multiple continuous grooves, having a depth (V2) smaller than100 micrometres, which are oriented in at least two different directionsto form a net-like geometry, wherein the pitch (V4) between twosuccessive and parallel grooves is between 0.1 mm and 0.2 mm.

In more detail as to the third variant (30 c, 40 c) of combinedroughening (FIGS. 12 a-b ), it is easily carried out by producing asheet provided with a porous surface (401 a-b, 411 a-b) according to atleast one of the above-described processes, wherein then said cutsurface (402 a-b, 411 c-d) is also made by means of a mechanical actionaccording to at least one of the above-described processes.

Finally, it is observed that each reference to said membranes of theroughened type (40, 40 b, 40 c), according to the above-described andrepresented embodiment configurations (FIGS. 9-16 ), is meant to beincluded in the advantageous embodiment configuration according toinvention (10 a, 10 b), in particular as in said detail sections (FIGS.3 a, 3 b, 4 a, 4 b ).

REFERENCE

-   (10) separating membrane of the bossed type, according to the    invention, in a first variant (10 a) with chambers provided with an    internal crown with flattened edges, or in a second variant (10 b)    with chambers provided with an internal crown with inclined lower    edge;-   (100) waterproof extruded sheet;-   (101) permeable base layer, of a nonwoven fabric;-   (102) boss, protruding from the lower face, in the cylindrical base    configuration (102 a) or double grouped (102 b) or triple grouped    (102 c);-   (103) internal chamber of the boss, open on the upper face;-   (104) internal crown, continuous and protruding to form a necking    which divides the chamber into two compartments, an upper    compartment above it and an undercut lower compartment, said crown    in the first variant having superimposed edges (104 a) or in the    second variant having the lower edge inclined (104 b);-   (105) upper compartment, above the crown;-   (106) lower compartment, which is formed by the necking,    corresponding to said internal crown, and by the underlying    widening;-   (107) widening below the internal crown;-   (108) upper edge of the internal crown;-   (109) lower edge of the internal crown, undercut;-   (110) upper face of the membrane, facing upwards;-   (111) lower face of the membrane, facing downwards;-   (112) contact surface between the head of the boss and the base    layer;-   (113) non-bossed surface of the sheet, at the extrados;-   (114 a) membrane portion in the base configuration with cylindrical    bosses; (114 b) membrane portion in the variant with two by two    grouped bosses; (114 c) membrane portion in the variant with three    by three grouped bosses; (114 d) membrane portion in the combined    variant, single-grouped; (200) forming roller;-   (201 a-b) protrusion which forms the boss, in the two variants for    forming the internal crown, respectively in the first variant with    superimposed edges (201 a) or in the second variant with inclined    lower edge (201 b)-   (202 a-b) main notch, intended to form the internal crown, in the    rectangular variant (202 a) or in the triangular variant at 45° (202    b);-   (203) secondary notch at the base of the protrusion, intended to    facilitate the forming of the boss; (204) first portion of the    protrusion of the roller, cylindrical, in correspondence of the    secondary notch;-   (205) second portion of the protrusion of the roller, cylindrical,    in correspondence of the greater diameter;-   (206 a-b) third portion of the protrusion of the roller in    correspondence of the internal crown, in the two embodiment    variants: cylindrical (206 a) with the smaller diameter, or shaped    as a truncated cone (206 b);-   (207) fourth portion of the protrusion of the roller, cylindrical,    in correspondence of the widening underlying the internal crown;-   (30 a-c) production process for roughening a bossed membrane,    according to the invention, realizing a roughening configuration of    the type: with porous surface (30 a), with cut surface (30 b) or    with both porous and cut combined surface (30 c);-   (40 a-c) roughened membrane, according to the invention, in a first    roughening configuration (40 a) with porous surface, or in a second    configuration (40 b) with cut surface, or in a third configuration-   (40 c) with both porous and cut combined surface;-   (400) plastic sheet;-   (401) porous roughening surface, in a first variant (401 a) with    superficial microcavities in the form of single micropores, or in a    second variant (401 b) with superficial microcavities in the form of    composite pores;-   (402) cut roughening surface, in a first variant (402 a) with    superficial microcavities obtained by brushing in the form of    discontinuous grooves or in a second variant (402 b) with    superficial microcavities obtained by grinding in the form of linear    and parallel grooves, in oriented bundles;-   (404) smooth surface;-   (405) boss protruding from the lower face;-   (406) internal chamber of the boss;-   (407) side walls of the boss;-   (408) head of the boss;-   (409) upper face of the membrane, that is to say, facing upwards;-   (410) lower face of the membrane, that is to say, facing downwards;-   (411 a-d) roughening superficial microcavities, in the variants of    the type micropores (411 a), composite pores (411 b), discontinuous    grooves obtained by brushing (411 c), linear and oriented grooves    obtained by grinding (411 d);-   (412) single crater;-   (413) multiple crater;-   (414 a-b) sub-craters joined to form a multiple crater;-   (415) mouth of the crater;-   (416) brushing removed chip;-   (417 a-b) primary and secondary grinding directions;-   (418) oriented bundle formed by a group of grinding superficial    microcavities, in the form of linear and parallel grooves, being    oriented according to a primary direction (418 a) and a secondary    direction (418 b); (a) relative angle between the direction of    protrusion of the upper edge of the internal crown and the inclined    lower edge;-   (ß) relative angle between the primary and secondary grinding    directions; (D1) greater diameter of the chamber inside the boss;-   (D2) smaller diameter, corresponding to the internal crown;-   (L) width of the internal crown;-   (H) total depth of the chamber;-   (HI) depth of the first compartment;-   (H2) depth of the second compartment;-   (H3) depth of the widening below the internal crown, in    correspondence of the fourth portion of the protrusion of the    roller;-   (P) pitch of the bosses arranged in a matrix;-   (SI) total thickness of the bossed sheet.-   (VI) width of the superficial microcavity;-   (V2) depth of the superficial microcavity;-   (V3) thickness of the sheet of plastic material;-   (V4) pitch between the superficial microcavities in the form of    parallel grooves obtained by grinding.

We claim:
 1. A process for producing a separating membrane with improvedadhesion for use in construction, the process comprising the steps of:extruding a raw plastic material so as to form a waterproofing plasticsheet, the raw material being a thermoplastic material or a mixture ofpolymers; forming the extruded plastic sheet around a bossed rollerhaving protrusions arranged in a regular matrix so as to form bosses inthe plastic sheet; and roughening one face of the plastic sheet byforming superficial microcavities by release of internal gas from theexternal surface of the plastic sheet, the superficial microcavitiesopening outwardly and having a depth of greater than 35 micrometers, thesuperficial microcavities being irregular craters or pores.
 2. Theprocess of claim 1, the step of roughening further comprising: forminggrooves or cuts in the one face of the plastic sheet by mechanicalremoval of portions of the plastic sheet.
 3. The process of claim 1,further comprising: prior to the step of extruding, adding an additiveto the raw plastic material so as to produce the internal gas releasedduring the step of roughening, the additive being a mineral filler or afoaming agent.
 4. The process of claim 3, the additive comprisingparticles of calcium carbonate of nanometric dimensions where 99% of theparticles have a diameter smaller than 50 micrometres, wherein theadditive quantity is between 1% and 20% of the total raw material, andwith a humidity lower than 0.5%.
 5. The process of claim 3, the additivecomprising a foaming agent between 0.25% and 2% of the total mixture ofraw material.
 6. The process of claim 5, wherein the foaming agent isazodicarbamide in a polyethylene matrix at 0.5% in weight when extrudingthe plastic material at 500 g/m².
 7. The process of claim 3, theadditive comprising a foaming agent between 2% and 5% of the totalmixture of raw material.
 8. A process for producing a separatingmembrane with improved adhesion for use in construction, the processcomprising the steps of: extending a raw plastic material so as to forma waterproofing plastic sheet, the raw material being a thermoplasticmaterial or a mixture of polymers; forming the extended plastic sheetaround a bossed roller having protrusions arranged in a regular matrixso as to form bosses in the plastic sheet; and roughening an entirety ofone face of the plastic sheet by forming grooves or cuts in the one faceof the plastic sheet by superficial mechanical removal of portions ofthe plastic sheet, the grooves or cuts comprising superficialmicrocavities opening outwardly and having a depth of greater than 35micrometers.
 9. The process of claim 8, the step of roughening furthercomprising: prior to the superficial mechanical removal of portions ofthe plastic sheet, forming additional superficial microcavities byrelease of internal gas from the external surface of the plastic sheet.10. The process of claim 8, the step of roughening comprising: passingthe bossed plastic sheet through thermal conditioning rollers withintegrated rotating means for brushing or grinding so as to form thegrooves or cuts.
 11. The process of claim 10, wherein the rotating meansfor brushing or grinding comprise a rotating shaft covered with metalbrushes.
 12. The process of claim 10, wherein the rotating means forbrushing or grinding comprise belt grinders arranged in series.